Conventional non-fluidized bed coffee roasting equipment uses a roasting atmosphere at a temperature often exceeding 540.degree. C. In addition, conventional non-fluidized bed roasters typically use low weight ratios of roasting atmosphere to coffee beans (hereinafter referred to as the air to bean ratio). The combination of the high roasting temperature and low air to bean ratio results in a temperature gradient from bean to bean as well as within the coffee bean itself. Such a temperature gradient indicates that different roasting reactions occur at different times among the beans as well as internally in any given coffee bean.
Fluidized bed roasting of coffee beans is well established in the art. For example, U.S. Pat. No. 4,169,164 to Hubbard et al. describes a two stage fluidized bed roasting process wherein the temperature in the first stage is between about 226.degree. C. and 243.degree. C. and the temperature in the second stage is between 268.degree. C. and 285.degree. C. A similar, improved process is disclosed in U.S. Pat. No. 4,322,447 to Hubbard wherein the temperature in both stages is between 287.degree. C. and 299.degree. C. although the velocity of the roasting atmosphere is varied between the two stages. The apparatus contemplated for use in both disclosures is a fluidized bed apparatus wherein heated gas is directed downwardly through jets onto a vibrating gas-impervious plate which gas is then deflected upward, thereby fluidizing the roasting coffee beans. The apparatus is more fully described in U.S. Pat. No. 3,229,377 to Hoyt. Numerous modifications of the apparatus are disclosed in U.S. Pat. Nos. 3,262,217, 4,109,394, 4,169,322, 4,201,499 and 4,306,359. Both the Hubbard and Hubbard et al. processes operate for at least a portion of the roast at temperatures well in excess of 240.degree. C. and hence, fail to gain the advantages of the present invention.
Another apparatus for the fluidized bed roasting of coffee at temperatures not in excess of 276.degree. C. is disclosed in U.S. Pat. No. 3,964,175 to Sivetz. Again, by roasting at temperatures as high as 276.degree. C., the Sivetz apparatus does not offer the unique advantages of the present invention. The Sivetz disclosure also contains an extensive survey of the prior art attempts at fluidized bed roasting. The processes described therein are unlike the present invention.
It is an object of the present invention to provide a coffee roasting method which permits better control of the final product properties.
It is another object of the invention to provide a roasting method which provides greater control over the roasted whole bean density.
It is another object of the invention to provide a roasting method to produce a less dense coffee having flavor strength and soluble solids yield equal or better than that of a denser conventionally roasted coffee.
It is a further object of the present invention to provide a roasting method with greater process control, owing to the lower roasting temperatures used therein.